1. Field of the Invention
The present invention relates to sailboards, universal joints for flexibly mounting rigs onto sailboards, and means to absorb vertical forces of a sailboard rig against a sailboard in choppy water.
2. Description of the Prior Art
In a conventional sailboard, the rig, which usually comprises a base cup, a mast base, a mast, a boom, and a sail, is attached to the board by a universal joint which permits the rig to be rotated a full 360.degree. with respect to the board. The conventional universal joint includes a concave cylinder of solid rubber which permits the rig to pivot anywhere from perpendicular to the plane of the board to parallel to the board. As is well accepted, this pivoting between rig and the board is essential to the basic operation of the sailboard. However, solid rubber universal joints are prone to failure due to the tendency of the rubber to "age" rapidly when exposed to sun, sand, and salt water and to wear and break as a result of the stresses placed upon them. Naturally, this tendency toward joint failure is increased under the increased stresses of rough water conditions.
Further, it is known that sailboards experience loss of efficiency in choppy water or after jumps due to essentially vertical forces created by the rig weight relative to the board. Basically, the vertical movement of the board causes the rig to move up and down. The absence of means to absorb the vertical forces of the rig creates a number of undesirable effects. First, the mast tends to flex to absorb these forces. This bending of the mast alters the trim of the sail and "spills" wind--thus decreasing the efficiency of the sailboard. Second, the downward forces of the rig causes deflection of the hull (i.e. the shape of the board itself alters to absorb impact), again diminishing efficiency. Finally, the constant jarring of choppy water places substantial stresses upon the rig, universal joint and board, which tends to significantly decrease the life of the sailboard equipment.
In response to these problems, one solution suggested is to incorporate a piston shock absorber unit into the mast or mast base itself which could absorb the forces of impact. The present inventor is unaware of any commercial embodiment of such a unit. One major problem with this approach is that the forces of impact are not always directed axially along a sailboard mast--especially during jumps or in rough water where the rig is often positioned at skewed angles with respect to the board. Accordingly, this shock absorber cannot absorb all the undesirable forces and the unit itself is necessarily subjected to lateral forces which may damage the piston.
Additionally, the expense of a piston shock absorber unit makes it deficient in many respects. In order to incorporate such a unit, substantial changes must be made to conventional masts or mast bases This presents undue expense--requiring the purchase of both the shock absorber unit and of modified rigs and hardware to employ the unit. Moreover, the relatively complex piston shock absorber is necessarily expensive to manufacture. This presents expense both in the initial purchase and in maintenance, especially in light of the extremely harsh sand and salt water conditions to which sailboard equipment is often subjected. Finally, further expense is encountered if the shock absorber unit is fitted with means to adjust the degree of shock absorbency.
In light of the foregoing, it is a primary object of the present invention to provide a shock absorber unit which absorbs substantially all forces exerted by a rig upon a sailboard and may be adjusted to control the amount of shock absorbency.
It is a further object of the present invention to provide a shock absorber unit which is relatively simple in design and inexpensive to manufacture, extremely durable, and may be readily employed with conventional sailboard equipment.
It is an additional object of the present invention to provide a shock absorber unit which also serves as a more durable and reliable universal joint for a sailboard.